Oil burner control variable resistance operated stack switch



March 7, 1939. H, c RQHR I 2,149,871

- on BURNER common wan-mm RESISTANCE OPERATED STACK swmcn Filed March 23, 1936 STACK THERMOSTAT' Patented Mar. 7, 1939 UNITED "STATES OIL BURNER CONTR ANCE- OPERATED STACK SWITCH L VARIABLE RESIST- Henry C. Bohr, Rochester, N; Y., assignor to (ieperal Motors Corporation, Detroit, Mich, a. corporation of Delaware Application March 23 I 1 Claim.

This invention relates to electric control circuits generally and more specifically to control circuits that are primarily adapted to be used for controlling various heating systems such as oil burners.

In designing a control circuit for oil burner operation there are certainfundamental operas tions which it is necessary to fulfill from a standpoint of safety of operation and these may be stated briefly as follows: 7

The apparatus must be completely turned off if,

First: The oil burner does not ignite upon an initiation of operation through thermostatic ac: tuation upon a call for heat from some control station.

Second: There must also be a provision for shutting down the whole system if at any time the flame is extinguished for any reason and,

Third: There must be a provision to throw the 2 system into safety if the currentis discontinued for even a short period of time.

With these primary factors in mind, it is the purpose of my invention to provide a circuit fulfilling these requirementsand at the same time being comparatively simple in construction.

For a better understanding of the nature and objects of my invention reference is made to the following specification wherein there are described the embodiments of my invention which are illustrated in the accompanying drawing, in

which:

The figure shows a diagrammatic wiring system of the circuit of my invention.

Referring specifically thereto, the source of our-- 5 rent is applied across lines 2, 4 and is applied to the primary 6 of the transformer generally designated at 8. To the line 4 is connected line Ill whose opposite end is connected to one contact I2 of a relay switch Hi. The contact l6 opposite contact i2 is connected by the line 22 to a rotatable needle 20 adapted to be rotated by the bimetallic stack element 2|. This needle 20 carries adjacent its outer end a contact 24 which cooperates with a stationary contact 26 connected to line 28 45 and thereby to one side of the actuating coll for the relay H, the opposite side of the relay coil being connected by line 36 to one side of the sec ondary 32 of the transformer 8. The end of the needle 20 moves along an arcuate path and is de- 5o signed to traverse a resistance heating coil 34 and to act with rheostatic action thereover to cut in or out of the circuit varying amounts of resistance.

One end of the heater coil is connected by line 55 36 to contact 36 which with its cooperating con- 1936, Serial No. 70,388

tact 40 is bridged by a switch member 42 which switch member may be termed the warp switch and is actuated by a bimetallic element whose position is controlled by the amount of heat supplied thereto by the heating coil. The term switches in this application is used in a broad, generic sense and they may either be mercury switches, contact switches, or any other type which it is deemed desirable to use. Contact 40 is connected by line 44 to one contact 46 of the room thermostat, the opposite contact 48 of which is'conne'cted through the thermostat andthrough a line 50 to the opposite side of the secondary 32. The movable armature l6 of the relay i4 is made of insulating material and carries thereon two movable contacts 52, 54; The contact 52 is connected to line 28 by line 56 and the opposite contact 54 is connected by line 58 to one terminal of a mercury switch 6|], the opposite terminal of which is connected by line 62 to a primary winding 64 of the ignition transformer, generally designated at 66, the opposite end of the coil 64 being connected by lines 68, 10 to the main line 2. A blower motor 12 is connected across the primary 64 and is connected toline 58 by line 14, the opposite side of the motor being connected directly to line Iii.

Adjacent the primary coil 64 of the ignition transformer is a secondary winding I6 across which is connected a spark gap 18 across which the charge is dispelled to cause a spark and thereby ignite the incoming oil. The bimetallic stack element 2| which as before mentioned rotates the needle 20, also has connected on its shaft means for operating or rotating the mercury tube 60, the

purpose of which will become evident as the description proceeds.

The operation of the device is as follows: Considering that all of the apparatus is in a condition of rest or de-energization, the room thermostat contacts 46, 48 are open as a sufi'icient temperature is present in the area to be heated. Switch 42 is closed across contacts 38, 40 as this element is normally in that position unless abnormal conditions are present to open said switch, after which it then requires a manual reset. The thermostatic element holds the needle 20 in the position shown and in which position contacts 24, 26 are closed. The relay is in its uppermost position which keeps contacts I8, 52 and i2, 54 open and the mercury switch is in its closed position. At this time therefore, the room thermostat closes contacts 46, 48 as the temperature drops sufllciently to require additional heat. A circuit is now completed from secondary coil 32 to line 50, room thermostat contacts 46, 48, line-44, switch 42, line 36, heating resistance coil 34, needle 20, contacts 24, 26,'line 28, relay coil l4 and line 30 back to the secondary. This current energizes the relay thereby attracting its armature which'closes contacts I8, 52 and also i2, 54. A circuit is completed through the last mentioned contactsto the motor which now begins to rotate through the following circuit: line 4, line I0, contacts I2, .54, line 58, line 14, motor 12 and line 10 back to the opposite incoming line 2. The motor therefore starts upat the time the motor circuit is completed.

A circuit is also completed through mercury switch 60, line 62, primary 64 of the i'gnitlon transformer and line 68 in addition to the various lines mentioned in connection with the motor to energize the ignition transformer whichcurrent of course is transmitted to the secondary winding 16 and sparks begin to jump across the gal 78 to ignite the oil. Therefore, considering normal operation, the oil is ignited and the temperature in the stack increases which afiects the stack bimetallic element which with the application of heat commences to rotate the needle 20 in a counterclockwise direction as shown in the drawing and at the same time turns the ignition switch 60 which after suflicient travel cuts out the ignition transformer. Therefore, as the-needle 20 passes over the resistance heating coil 34'it cuts out more and more of the current until there is an insufiicient amount left to supply enough heat to throw out the warp switch.

It will also be noted that as soon as the needle 20 moves it b;eaks contacts 24,. 26 but contacts I8, 52 closing provides a shunt around the contacts 24, 26 so that their opening will now cause no change. If for any reasonthe burner does not start and the oil does not ignite, there will be no increase in the temperature and therefore the needle 20 will remain on the right-hand portion of the heating coil and the passage of the current through the coil 34 will heat up the same and after a predetermined time interval the warp switch 42 will open.

Considering that the burner is. operating normally and delivering heat and there is a flame failure for any reason such as a certain amount of water or air in the oil, the following operation will take place:

The burner motor will continue to run but the this connection that while the stack switch. element incooling down returns the needle 20 in a clockwise direction, that there is provided a mechanical interlock to prevent the return of the mercury switch at this time so that ignition "may not come 'on' under these conditions but that "the burner will be shut down.

If there is a. momentary failure of current when the burneris operating normally the relay will at once bede en'ergized and its armature will cause the contacts I8, 52 and I2, 54 to be broken and since the needle '20 is in a position adjacent the left-hand portion of the heating coil due to the forces supplied by the stack element, the contacts 24, 26 will be opened. There will be no circuit by which the relaymay again be ener-' gized until the stack switchhas cooled suificiently to close contacts 24, 26, which will therefore givea time delay to allow the heated vapors to clear from the furnace before the device againrecycles. 1

It is therefore evident that I have provided a simple'circuit which fulfills the various requirements of safety as previously set forth. v I claim: I l In a control system for fuel burners, a high and a low voltage circuit, a fuel propelling means and a switch therefor in the high voltage circuit; a room thermostat, switch contacts, electrical heating coil for actuating said contacts and a relay coil all in series in the lowvoltage circuit, said relay actuating the high'voltage switch, a member movable over the heating coil to vary the amount thereof in circuit, a stationary contact, a contact cooperating therewith on the movable member, said member closing the pair of contacts at one extremityof its travel, means'for moving the member actuated by combustion temperature, a "shunt circuit around the lastnamed contacts and apair of contacts in said shunt circuit actuated by the relay coil simultaneously with the high voltage switch whereby a startingand a holding circuit is'provided for'the relay coil. I

HENRY C. RQHR. 

